1. Field of the Invention
This invention relates generally to mechanical seals and, more specifically to cartridge mounted mechanical seals which.
2. Prior Art
Mechanical seals are used to provide a seal between various components on a rotating shaft. Such seals take many different forms. In the field of cartridge mounted seals are mechanical seals which have at least one set of contacting seal faces, one rotary face and one stationary face, the rotary face being driven by its connection to a sleeve which is mounted nonrotatably to the shaft. The entire cartridge seal unit is installed by simply sliding the sleeve and the attached seal components onto the shaft and fixing the sleeve in place. A gland plate is provided for supporting the stationary seal face. The gland plate is usually bolted to the housing (such as a pump housing) through which the shaft extends.
Cartridge mounted mechanical seals are shipped and installed as a unit. The rotary sleeve of the seal and the lock collar of prior art seals are held in place during shipment by temporary clips or cams, which work in conjunction with set screws which are threaded through holes in the lock collar and the sleeve. A typical arrangement is shown in FIGS. 3 and 4. Cup point set screws 60 extend through lock collar 61 and sleeve 62. Upon installation, cup point set screws 60 dig into shaft 63, setting the seal in position. Although some seals have only cup point set screws to both set and drive the seal, this is not desirable. As shown in FIGS. 3 and 4, dog point set screws 64 having a blunt end are installed through holes in the lock collar 61 and the sleeve 62. The hole in sleeve 62 matingly receives the end of dog point screw 64. Thus, the lock collar 61 receives torque from the cup point set screws 60 and drives the sleeve 62 via the dog point screws 64, protecting the cup point screws 60 and threads from excessive wear. Dog point screws 64 also provide a means for maintaining axial alignment of seal parts during shipment.
While the dog point set screws 64 solve the problem of excessive wear of the cup point screws 60 as well as maintain axial alignment, several other problems present themselves. It is difficult to determine from the exterior of the lock collar 61 which screws are which, resulting in accidental loosening or tightening of the wrong screws. For example, a dog point screw 64 may be overtightened to the point where the blunt end of the screw abuts the shaft, causing the lock collar 61 and/or the sleeve 62 to bend. Further, during rotation of shaft 63 dog point screws 64 may back out of their holes causing excessive torque to be transmitted to cup point screws 60, galling threads and damaging the seal. Also, should dog point screws be mistakenly removed or loosened during shipment, axial misalignment of the seal can result.